1. Field of the Invention
The present invention relates to a passive optical network (PON), and more particularly to a wavelength-division-multiplexed PON (WDM PON) using a wavelength-locked optical transmitter.
2. Description of the Related Art
A wavelength-division-multiplexed passive optical network (WDM PON) allocates a dedicated wavelength to each subscriber to provide an expandable and secure ultra high speed broadband communication services.
In order to reduce costs for realizing the WDM PON, one type of an optical transmitter has been used. At the same time, there exist efforts for using a plurality of the optical transmitters capable of outputting optical signals with various wavelengths instead of a specific wavelength. In particular, the following schemes have been suggested to use one type optical transmitter.
A first scheme is to spectrum-slice broadband optical signals output from a plurality of the optical transmitters in a wavelength division multiplexer. A second scheme is to obtain a wavelength-locked optical transmitter by injecting a light having a specific wavelength into each optical transmitter.
U.S. Published Application No. 2005/0286895 filed by Lee, Chang-Hee discloses “Bi-directional wavelength-division-multiplexing passive optical network (WDM PON) utilizing wavelength-locked light sources by injected incoherent light”. Briefly, the WDM PON in Lee includes combination of an upstream broadband light source, a downstream broadband light source, and an optical coupler in order to generate an optical signal having a specific wavelength by injecting incoherent light into an optical transmitter. The optical transmitter may be a Fabry-Perot laser diode or a reflective semiconductor optical amplifier (RSOA). In addition, the WDM PON using a wavelength-locked optical transmitter controls the power of an injection light, so that it is possible to improve the transmission quality, which also serves to enhance the transmission rate.
As described above, since the conventional WDM PON uses combination of an upstream broadband light source, a downstream broadband light source, and an optical coupler in order to obtain a wavelength-locked optical transmitter, costs associated with the WDM PON and the power reinforcement of an injection light may be increased.
Accordingly, there is a need for a WDM PON using a wavelength-locked optical transmitter capable of ensuring a high quality at low costs.